Real-time communication systems include communication systems that guarantee delivery of communication message data within predetermined time limits. Real-time communication systems are used in a wide range of applications, with industrial control systems being one example where real-time communications are important to the successful operation of manufacturing, control, automation, and other industrial processes.
Existing wireless communication systems are not suitable for the real-time operational requirements of industrial applications that include real-time communication requirements between multiple devices. For example, wireless networks including a large number of wireless communication nodes require shared access to a wireless communication medium. In existing wireless communication systems, any node may transmit at any time, with collisions occurring between two or more nodes that transmit simultaneously. Intelligent solutions sense the wireless channel before transmitting to avoid collisions and are thus non-deterministic. Therefore, the existing wireless systems provide no guarantees that each node has an opportunity to transmit a predetermined amount of data within a bounded time period.
Techniques for allocation of a shared communication medium to multiple communication nodes exist, but suffer from inefficiency. As depicted in FIG. 1, a simple brute-force time-division multiple access (TDMA) method guarantees transmission time to each of N slave communication nodes through assignment of one time slot in a series of N equal time slots to each node. Each slave wireless node transmits data to the master wireless node in a designated time slot. The time slots repeat every N slots, and each node waits for the next corresponding time slot to transmit data. For large numbers of nodes N, the time delay between time slots in which a node may transmit data increases until the time delay is unacceptably large for use with the wireless communication network. In FIG. 2, another prior art TDMA system includes multiple radio channels where subsets of the N wireless nodes each communicate using time slots using one of a plurality of independent radio channels. FIG. 2 depicts an example with two radio channels. Multiple radio channels enable the master wireless node to send and receive to N slave wireless nodes, but the additional radio channels require additional wireless frequency spectrum. Implementing a master wireless node that is configured to use a large number of channels concurrently as depicted in FIG. 2 requires more complex hardware that is often impractical in large-scale wireless networks.
While existing TDMA systems enable communication between multiple slave wireless nodes and a master wireless node, inefficiencies in communication remain. For example, in some wireless networks, the slave wireless nodes send short messages including small amounts of data to the master wireless node. Each communication between the master wireless node and a slave wireless node includes a fixed communication overhead, with examples of overhead including communication protocol handshake data, and message preamble data, and connection setup and teardown data for connection based protocols. The time required for the fixed overhead in each transmission is typically independent of the size of the message so, for example, the fixed overhead for a message that includes a single byte of data is typically the same as the fixed overhead for transmitting 1,000 bytes of data. Since a wireless communication network or any other network can only transmit data at a finite speed, the requirement to transfer data as part of the fixed overhead increases the total time required to transmit a message. In some wireless communication networks, the fixed overhead for node-to-node communication forms a substantial fraction of the time required to send and receive data in the wireless network. Consequently, improvements to the configuration of wireless networks that reduce the total fixed overhead for communication during communication between slave wireless nodes and a master wireless node would be beneficial.